CLEARWATER — On a summer night nearly three years ago, the roar of a racing engine reverberated on Clearwater Beach's Mandalay Avenue, and Jonathan Grinsted's Toyota Land Cruiser zoomed up onto the sidewalk, smashing into an office and killing a woman who was sitting on the curb.

Ashley Boyle, 44, a lifelong Clearwater resident, was sitting there with a friend to escape the rain.

It seemed likely that Grinsted, then 51, would spend many years in prison because of the crash. Tests showed his blood alcohol level was 0.14, well over the 0.08 level at which drivers are presumed impaired. He was arrested on a charge of DUI-manslaughter, a felony that carries a possible sentence of 15 years in prison.

But Thursday, in an unusual move, prosecutors allowed Grin­sted to plead no contest to a greatly reduced charge of misdemeanor DUI. Instead of prison, he will serve 12 months probation.

What makes this case different from so many others involving drunken driving and death?

Defense attorney Denis de Vlaming gave this answer: sudden acceleration problems in Toyotas.

The issue led to widespread news coverage in recent years as complaints mounted about Toyotas accelerating unexpectedly. It culminated last year when the auto giant agreed to a $1 billion deal to settle hundreds of lawsuits.

Grinsted did not dispute that he was intoxicated at the time of the crash. But his drinking was not the cause of the accident, de Vlaming maintained.

"If he was stone sober, this would have happened," de Vlaming said. "He individually as a person did not cause this accident."

De Vlaming explained the case this way:

Grinsted's Land Cruiser previously had problems with sudden acceleration. The year before, it accelerated suddenly and smashed through the garage door at his home.

Grinsted had the SUV fixed, but another time a warning light came on the dashboard concerning the acceleration. He took it in for repairs, but the problem seemed to come and go.

On a Sunday evening in July 2010, Grinstead got into the SUV, which he had parked near 604 Mandalay Ave.

Nearby, Boyle was sitting on the curb with a friend, after an afternoon on the beach. They had ducked under a nearby awning to get out of the rain.

Witnesses said they heard the Toyota's engine racing. Grinsted would later say "the car took off, it just took off," veering onto the sidewalk and striking Boyle, de Vlaming said.

After the crash, de Vlaming hired a forensic engineer to investigate. With a master mechanic and an expert brought in by the State Attorney's Office, they dismantled and examined the "throttle control module," and discovered problems that could lead to unusual acceleration.

Assistant State Attorney Holly Grissinger said prosecutors at first rejected the theory that sudden acceleration caused the accident. But as the criminal case progressed, so did the civil cases against Toyota. Toyota eventually issued recall notices related to that problem in the very same type of SUV Grinsted was driving.

That made it impossible for prosecutors to prove the cause of the crash was "the defendant's intoxication versus the unintended acceleration of the faulty vehicle," Grissinger said. In fact, similar decisions have been made in other criminal cases around the county, she said.

Both lawyers said to prove the charge of DUI manslaughter, it would not be enough to prove that Grinsted was driving drunk. It also would be necessary to prove his drunkenness caused the accident, as opposed to some other cause, such as a malfunctioning vehicle.

A friend of Boyle's spoke at the plea hearing on Thursday, displeased with the result. He could not be reached afterward.